Optical sights are used for various purposes, one example of which is mounting a sight on a weapon in order to help a user accurately aim the weapon. The optical sight takes image information from a distant scene, and presents this image information within a field of view which is visible to the eye of a user.
In some situations, it is desirable to be able to provide some supplemental information within this same field of view, such as alphanumeric information generated by circuitry within the sight. For example, the sight might include a laser rangefinder which can determine a distance to a target, and then generate alphanumeric indicia representing this distance. One possible approach for showing supplemental information of this type to a user would be to present it on a display which is physically and spatially separate from the sight's optical field of view. However, this would force the user to take his or her eye off the target or scene in order to observe the supplemental information.
A different approach would be to use an image detector to digitize the optical field of view containing information from the scene, then use a microprocessor to digitally combine this information with the supplemental information, and then display the combined information on a digital display such as a color liquid crystal display (LCD). However, existing full-color LCDs are sometimes difficult to see in direct sunlight. Further, in the event of a battery power loss, the entire sight becomes non-functional.
Still another possibility would be to use a wideband beam splitter to inject the supplemental information into the sight's optical field of view. However, this would cause a significant portion of the brightness of the sight's optical image to be lost. As a result, there would be a significant degradation in the transmission efficiency of this radiation, which in turn would significantly reduce the utility of the sight in low light conditions, such as at dawn and dusk.